Field of the Invention
The invention pertains to foam material elements and, specifically, to a foam material element for sound-damping cavities. More particularly the element is provided for sound-proofing extruded profiles of metal or plastics material. The element is compressed prior to being inserted into a cavity, weld-sealed in an air-tight film so that it can be inserted through an opening into the cavity. After being inserted, the sealing film is opened and the foam material element expands in air so that it comes into contact with at least two walls of the cavity.
Increasing demands are placed on more lightweight structures of rail vehicles, for both ecological and economic reasons. As a result, more and more lightweight materials are being used in the construction of rail vehicles. Hollow-chambered extruded profiles of light metal, in particular of aluminum materials, are well suited for car box structures. The drawback in using such extruded profiles is the noise they allow to develop. Aluminum extruded profiles have practically zero sound damping, that is flexural waves excited in the corresponding car box structure decay only very slowly and they propagate throughout the complete structure practically without obstruction. This results in a drumming noise (rumbling, roaring) in the car box structure. In addition, two-shell components, such as the above-mentioned extruded profiles, are subject to breakdowns in the sound damping. This phenomenon is termed coincidental breakdown. In two-shell extruded profiles with a land thickness of 2 to 5 mm and a land spacing of typically 20 to 70 mm these breakdowns lie in the audible range and thus have a negative effect on the sound damping behavior.
The drumming behavior of extruded profiles has been fought in the art by applying heavy films of bitumen or plastics to the outer wall of the extruded profiles cavities by spraying, wrapping or bonding.
It has become known in automotive engineering to eliminate air noise such as whistling and the like in cavities by the use of foam material elements in the vicinity of axle bearings. Those elements comprise soft foam material bonded to a carton material. Prior to being inserted in the cavity to be sound deadened the foam material element is available in a compressed condition and is weld-sealed in an air-tight film. In this compressed condition the foam material element can be easily inserted into the cavity through an access opening. Following insertion in the cavity air ingress is made possible by opening the film (for example by tearing or puncturing it open) so that the foam material element expands into a shape that comes into contact with at least two of the cavity walls. That prior art foam material element is suitable only for damping airborne noise, but not for damping material-borne noise, i.e. for anti-drumming.